feat: add shell integration

[sigoden]

This is a very handy feature, which allows you to use aichat shell completions directly in your terminal, without the need to type aichat with prompt and arguments. This feature puts aichat completions directly into terminal buffer (input line), allowing for immediate editing of suggested commands.

To install shell integration, run the following code:

sh_ext=bash # possible values: bash, fish, zsh, ps1
curl -o aichat-integration.$sh_ext https://raw.githubusercontent.com/sigoden/aichat/main/scripts/integration.$sh_ext
. aichat-integration.$sh_ext